The reasons why Firefox kicks ass are many and well documented, but the one relevant to this topic is its extensibility. GreaseMonkey is one such extension. Wired has a good article on it, but if you’re lazy…
GreaseMonkey allows Firefox users to use site-specific scripts to alter the look or behavior of websites that they visit. For instance, if you use Netflix, but you like to read about movies on IMDB, you can enable a script to display a “Add to my Netflix queue” link on each movie page on IMDB. Another script bypasses the interstitial ad pages and in-content ads on IGN.com. Well done geeks!